1. Field of the Invention
The present invention relates to a portable transmitter, which is advantageously used as a transmitter in a keyless-entry system for an automobile and in a keyless-starter system.
2. Description of Related Art
In a portable transmitter for the keyless-entry system, a battery is usually contained in a transmitter case. Under a normal condition where the battery voltage is normal, a door key of an automobile is locked or unlocked when an ID code (an identification code) sent form the transmitter coincides with an ID code pre-installed in the automobile. Under an abnormal or emergency condition where the battery voltage is too low to operate the system, a mechanical key contained in the transmitter case is taken out to lock or unlock the door.
Usually, the battery and the mechanical key are contained in respective spaces formed in the transmitter case. The battery, for example, is loaded from an opening, and the opening is closed with a battery cover. A seal member such as an O-ring is disposed around the opening between the case and the battery cover to keep the inner space water-tight. The battery cover is fixed to the case with screws so that the battery cover can be removed when necessary for changing an old battery to new one. Alternatively, the battery cover is snap-fitted to the opening.
In such conventional structures for containing the battery or the mechanical key in the case, the following problems are involved. If the battery cover is fixed to the case with screws, the heads of screws expose to the outer surface of the transmitter case, which damages an ornamental design of the case. If the battery cover is snap-fitted to the opening, the battery cover will come off from the case when the user of the transmitter inadvertently drops it on the ground. Further, the battery cover may be deformed by heat stress under an influence of repulsive force of the O-ring compressed between the case and the battery cover, which also damages the ornamental design. A similar problem will be involved in the space for containing the mechanical key.